For various reasons, including ill health, injury or surgery, patients may require substitution in the form of replacement or supplementation of the patient's natural kidney function in order to remove waste liquids from the patient's system. Such liquids would include excess liquids (due to the regulated addition of prescribed liquid or other liquids required to sustain the patient) and liquids containing dissolved waste products entrained in the patient's blood. There are several procedures used for the above purpose and include, hemodialysis, hemofiltration, and ultrafilation. All of these procedures result in the removal of waste products from the patient. Essentially the patent's blood is passed through a filter or membrane from which the waste liquid is removed and the blood is passed back into the patient. The replacement or augmentation of the patient's natural renal function can affect the balance of the body chemistry. In particular, the removal of waste liquids must be carefully controlled.
One of the procedures used for critically ill or injured patients is continuous arteriovenous or venovenous hemodialysis (CAVH or CVVH--in general CRRT, continuous renal replacement therapy). In these procedures the patient is on dialysis twenty-four hours per day, seven days per week for extended periods of time. CRRT is similar to hemodialysis, except that the patient is on the machine (the filter system) continuously rather than for several hours at varying increments of time. In CRRT, it is important to keep accurate records of dialysis liquids and intravenous liquids entering the patient and the amount of liquids leaving the patient. That is, a mass balance must exist when drawn about the patient. Severe clinical problems, and even death, may occur if these fluid balances are not carefully regulated.
Therefore, it is critical in CRRT to monitor, regulate and control the rate and volume of liquid removal from the patient.